Presently, the depletion of the ozone layer and global warming are listed as social and environmental problems on a worldwide scale. It is pointed out that chlorofluorocarbon used in refrigerators such as air-conditioners, etc. is responsible for the depletion of the ozone layer, and the abolition of a specified chlorofluorocarbon within the year of 1995 was prescribed in the international conference called in Montreal in 1987. However, a so-called alternative for chlorofluorocarbon, which is recognized to use as a substitute of the specified chlorofluorocarbon, produces an effect of warming several thousands to several tens of thousands times that of carbon dioxide, and became the object of reduction in the Kyoto Convention for prevention of global warming in 1997. In Europe, the future abolition of car-mounting of the alternative for chlorofluorocarbon has already been prescribed. Under such situation, the development of refrigerating and air-conditioning equipment, which is energy-saving and imposes a low environmental load, has become of urgent necessity, and attention begins to be paid to magnetic refrigeration, in which no chlorofluorocarbons are used. Magnetic refrigeration is conventionally made wide use of in obtaining very low temperature. However, practical use has been difficult in the ordinary temperature range because of a large heat capacity due to lattice vibration of a working substance and because of a large energy due to thermal agitation of a magnetic system. A magnetic material being inexpensive and producing a large magnetocaloric effect is needed as a material for magnetic refrigeration at ordinary temperature Gd (gadolinium) having a point of magnetic transformation (Curie temperature) around ordinary temperatures is conventionally known as a material for magnetic refrigeration at ordinary temperature. However, Gd is a rare and expensive metal among rare earth elements and thus is not an industrially practical material. In recent years, attention is paid to a magnetic material which shows metamagnetism transition, as a material for magnetic refrigeration at ordinary temperature, which replaces Gd. A magnetic material for magnetic refrigeration, which shows metamagnetism transition, is a material which undergoes magnetic transformation from paramagnetism to ferromagnetism upon application of a magnetic field around a Curie point, and provides a large magnetization change in a relatively weak magnetic field so that it posses a feature in that a large magnetocaloric change is obtained. Gd5Si2Ge2, Mn(As1−xSbx), MnFe(P1−x Asx), La(Fe—Si)13Hx, etc. are proposed as such magnetic material. Taking material cost, environmental load, safety in manufacturing processes, etc. into consideration, a La(Fe—Si)13Hx alloy among these working substances for magnetic refrigeration at ordinary temperature is thought to be a most promising candidate substance as a practical material. Examination mainly centering on material study is made on the material in universities (see Non-Patent Documents 1 and 2). Also, Patent Documents 1 and 2, etc. describe similar substances for magnetic refrigeration.
La(Fe—Si)13Hx, described above, being a material for magnetic refrigeration at ordinary temperature has expanded crystal lattice and raised Curie temperature by interstitially solid-solute hydrogen into La(Fe—Si)13 crystal lattice, which has a NaZn13 type crystal structure. As an industrial manufacturing method of the material, it is examined to obtain a desired La(Fe—Si)13Hx alloy by beforehand fabricating a single phase La(Fe—Si)13 mother alloy and solid-solute hydrogen between lattices through the gas-solid phase reaction (see Non-Patent Document 3). Hydrogen is solid-solute between lattices whereby the material for magnetic refrigeration at ordinary temperature is enlarged in crystal lattice and raised in magnetic transformation temperature to function as a working substance for magnetic refrigeration at ordinary temperature. For this purpose, it is required that hydrogen be uniformly dispersed and solid-solute into La(Fe—Si)13 being a mother alloy. Non-Patent Document 4 discloses, as means for solid-solution of hydrogen into a mother alloy, regulation of amount of solid solute hydrogen and control of magnetic transformation temperature by performing storage of hydrogen in high pressured hydrogen to absorb hydrogen up to around saturation, then performing heat treatment in an argon atmosphere, and performing a dehydrogenation processing.
[Patent Document 1] JP-A-2003-96547 ([0035] to [0037])
[Patent Document 2] JP-A-2002-356748 ([0050] to [0057])
[Non-Patent Document 1] Solid State Physics, vol. 37, (2002), 419
[Non-Patent Document 2] METAL, vol. 73, (2003), 849
[Non-Patent Document 3] Appl. Phys. Lett. 79 (2003) 653
[Non-Patent Document 4] NEDO Research Finding Report for the 14th year of Heisei (last edition) Project ID00A26019a